Glow discharge polymerization coating of toners for electrophotography

ABSTRACT

The triboelectric properties and minimum caking temperature of particulate toner material can be altered by glow discharge treatment in the presence of an inert gas, air or a gaseous polymerizable material.

United States Patent Wright et al.

[ 1 July 11,1972

[54] GLOW DISCHARGE POLYMERIZATION COATING OF TONERS FORELECTROPHOTOGRAPHY [72] .lnventors: John F. Wright; James R. Olson, bothof Rochester, NY.

Eastman Kodak Company, Rochester, NY.

22 Filed: Feb. 3, 1970 21 App1.No.: 8,424

[73] Assignee:

[52] U.S.Cl. ..252/62.1, 117/175,117/93.1GD,

[56] References Cited UNITED STATES PATENTS 3,090,755 5/1963 Erchak eta1 ..252/6 1.1 3,392,139 7/ 1968 Dengmon ..260/41 3,507,686 4/1970Hogenboch... 1 17/100 3,387,991 6/1968 Erchak 1 17/93. 1 3,247,0144/1966 Goldberger et al. ..1 17/ 1 00 3,447,950 6/1969 Evans et al 117/100 3,526,533 9/1970 Jacknow et al. ..1 17/100 3,440,085 4/1969 Bakeret a1 ..1 l7/l00 3 ,461,092 8/1969 Story ..260/28 3,533,829 10/1970Quanquin ..11/62 2 3,326,177 6/1967 Taylor ..1 18/49.

Primary Examiner-George F. Lesmes Assistant Examiner-John C. Cooper, [I]Attomey-W. H. J. Kline, J. R. Frederick and T. Hiatt 57 ABSTRACT Thetriboelectn'c properties and minimum caking temperature of particulatetoner material can be altered by glow discharge treatment in thepresence of an inert gas, air or a gaseous polymerizable material.

8 Claims, No Drawings GLOW DISCHARGE POLYMERIZATION COATING OF TONERSFOR ELECTROPHOTOGRAPHY such as by a corona source and an imagewise lightexposure that discharges the photoconductor in the exposed areas, anelectrostatic charge image remains. This electrostatic image, as well aselectrostatic images produced by other techniques, can be renderedvisible by treatment with an electrostatic developing composition ordeveloper. Conventional dry developers include a carrier that can beeither a magnetic material such as iron filings, powdered iron or ironoxide, or a triboelectrically chargeable, non-magnetic substance likeglass beads or crystals of inorganic salts such as sodium or potassiumchloride. As well as the carrier, electrostatic developers include atoner that is usually a resinous material suitably colored or darkenedfor image viewing purposes with a colorant such as dyestuffs orpigments, for example, carbon black.

To develop an electrostatic image, the dry developer can be appliedimagewise to the electrostatically charged surface by varioustechniques. One such technique is known as cascade development and isdescribed in U.S. Pat. No. 2,618,552. This development technique iscarried out by rolling or cascading across the electrostatic latentimage bearing surface, a developing mixture composed of relatively largecarrier particles, each having a number of electrostatically adheringfine marking particles, known as toner particles, on its surface. Asthis mixture rolls across the image-bearing surface, the toner particlesare electrostatically deposited on the charged portions of the image.

Another suitable developing technique is known as magnetic brushdevelopment and is described in U. S. Pat. No. 3,003,462. Thisdevelopment technique involves the use of a magnetic means in connectionwith a developing mixture composed of magnetic carrier particles havinga number of smaller electrostatically adhering toner particles. In thistechnique the developer composition is maintained during the developmentcycle in a loose, brushlike orientation by a magnetic field surrounding,for example, a rotatable non-magnetic cylinder having a magnetic meansfixedly mounted inside. The magnetic carrier particles are attracted tothe cylinder by the described magnetic field, and the toner particlesare held to the carrier particles by virtue of their oppositeelectrostatic polarity. Before and during development, the toneracquires an electrostatic charge of a sign opposite to that of thecarrier material due to triboelectric charging derived from their mutualfrictional interaction. When this brushlike mass or mag netic brush ofcarrier and toner particles is drawn across the photoconductive surfacebearing the electrostatic image, the toner particles areelectrostatically attracted to an oppositely charged latent image andform a visible toner image corresponding to the electrostatic image.

in typical electrophotographic applications, the developed image formedon a photoconductive element is transferred to a receiving sheet. Theimage thus transferred is then made permanent by heating to fuse thetransferred image. Thus, the resin of the toner material must be capableof being fused under temperature conditions which will avoid any.charring, burning or other physical damage to the receiver sheet whichis typically formed of paper. A variety of resin combinations have beensuggested in the art which allegedly will provide suitable fusionproperties. However, if the fusion temperature is sufficiently low, itis often found that the caking temperature of the toner material is alsovery low. This latter property is undesirable in that the toner materialcan readily be sintered or caked during storage or shipment. If cakingof the toner occurs, it can render the material totally unusable.

In addition, when toner materials are prepared using various resincompositions which have suitable fusion properties, it is quite commonthat the resultant toner materials have poor triboelectric chargingproperties. It is extremely important that the resultant toner materialbe capable of being triboelectrically charged either positively ornegatively depending upon the particular use and particular carrier withwhich it is mixed. If the toner material does not charge properly, itwill result in a poor quality developed image. A further problem whichcan result is that the toner material will not be triboelectricallyattracted to the carrier material with which it is mixed. This latterinstance will result in the toner material settling to the bottom of thecontainerv of developer mixture rather than being carried to the elementtobe developed. Thus, the end result in this instance could be that noimage at all will be developed using a mixture of this type.

Accordingly, there is a need in the art for toner materials which havegood fusion properties, a reduced tendency for the toner to cake andimproved triboelectric charge properties.

It is, therefore, an object of this invention to provide new dry tonercompositions for use in developing electrostatic charge patterns.

An additional object of this invention is to provide new electrostatictoner compositions which exhibit reduced caking tendencies.

A further object of this invention is to provide new dry toner materialswhich have improved triboelectric charging properties.

Still another object of this invention is to provide new dry developercompositions for use in development of electrostatic images.

A still further object of this invention is to provide novel processesfor treating dry toner material for use in developing electrostaticcharge patterns.

These and other objects are accomplished in accordance with thisinvention by the glow-discharge treatment of dry particulate tonermaterial typically comprised of a colorant and a thermoplastic resin.Particles useful for forming the toner materials of the presentinvention can be prepared by various methods. Two convenient techniquesfor producing these particles are spray-drying or melt-blending followedby grinding. Spray-drying involves dissolving the polymer and a colorantin a volatile organic solvent such as dichloromethane. This solution isthen sprayed through an atomizing nozzle using a substantiallynonreactive gas such as nitrogen as the atomizing agent. Duringatomization, the volatile solvent evaporates from the airborne droplets,producing particles of uniformly dyed resin. The ultimate particle sizeis determined by varying the size of the atomizing nozzle and thepressure of the gaseous atomizing agent. Conventionally, particles ofdiameter between about one-half and about 25p. are used, with particlesbetween about 2p. and l5p. being preferred, although both larger andsmaller particles can be used where desired for particular developerconditions or developer compositions. As mentioned above, suitableparticles can also be prepared by melt-blending. This technique involvesmelting a powdered form of polymer or resin and mixing it with asuitable colorant and any other desired additives. The resin can readilybe melted on heated compounding rolls which are also useful for stirringor otherwise blending the resin and other addenda in order to promotethe complete intermixing of the various ingredients. After thoroughblending, the mixture is cooled and solidified. The resultant solid massis then broken into small pieces and finely ground to form afree-flowing powder. The resultant particles usually range in size fromabout one-half to about 25 u.

The choice of starting polymeric materials is quite large in that avariety of materials may be used which heretofore would have beenunsuitable. A wide variety of materials can be used and the choice ofone material is not strictly limited by the caking temperature of thematerial or its triboelectric charging properties. Thus, materials whichpreviously were not suitable for use in toner compositions can inaccordance with the present invention be utilized. Useful resins have aninherent viscosity of from about 0.10 to about 0.4. The inherentviscosity is determined at C in accordance with the followwherein 1;solution is the viscosity of the solution, '1 solvent is the viscosityof the solvent and C is the concentration in grams of the polymer in 100ml. of chloroform. Useful resin materials can include natural andsynthetic resins. Styrene and styrene-containing polymers, alkyd resins,including modified alkyd resins such as rosin-modified maleic alkydresins, various polyolefins, such as polyethylene, polypropylene, etc,and the like are among the many polymeric materials which can beutilized in accordance with the present invention.

The colorants useful in the practice of this invention can be selectedfrom a variety of materials such as dyestufis or pigments. Suchmaterials serve to color the toner and thus render it more visible.Suitable toner materials having appropriate caking and chargingproperties can, of course, be prepared without the use of a colorantmaterial where it is desired to have a developed image of low opticalopacity. ln those instances where it is desired to have high opticalopacity, the colorants used, can, in principle, be selected fromvirtually all of the compounds mentioned in the Color Index, Vol. I andll, Second Edition. Included among the vast number of useful colorantswould be such materials as Hansa Yellow G (CI. 11680), Nigrosine Spiritsoluble (CI. 50415), Chromogen Black ETOO (CI. 14645), Rhodamine B (CI.45170), Solvent Black 3 (CI. 26150), Fuchsine N (CI. 42510), C]. BasicBlue 9 (CI. 52015), etc. Another useful class of colorants is comprisedof nigrosine salts such as nigrosine salts of mono and difunctionalorganic acids having from about 2 to about 20 carbon atoms such aschloroacetic acid, stearic acid, sebacic acid, lauric acid, azelaicacid, adipic acid, abietic acid and the like. Nigrosine salts of thistype are disclosed in copending application Ser. No. 736,552, filed June13, 1968, now abandoned, in the name of James R. Olson and entitledUNIFORM POLARITY RESIN ELECTROSTATIC TONERS.

After suitable resin-containing particles having the proper size aremade, these particles are subjected to a glowdischarge treatment inaccordance with the present invention. The term glow dischargetreatment" in connection with this invention has reference to anysuitable means of subjecting the particles to activating radiation tocause surface crosslinking or polymerization. Useful means of activationwould include direct current, electrodeless radio frequency, microwaveglow discharge, as well as ultraviolet radiation and electronbombardment.

The apparatus involved in the glow discharge treatment of the presentinvention is relatively simple. The actual treatment takes place withina reaction vessel which can readily be evacuated. The reaction vessel orchamber usually contains two parallel, closely spaced plate electrodes.When an ac. or do field of the order of several hundred v/cm is imposedon the parallel electrodes, a uniform discharge occurs between theplates and a thin, polymeric film is deposited on any materialmaintained between the electrodes. In one useful arrangement, theelectrodes are connected to a power source capable of maintaining atleast a 10 kc. a.c. field sufficient to produce a glow between theelectrodes. Also present is a means for containing the particles to betreated and maintaining them in a position between the electrodes. Asuitable means for this purpose is a filter paper diaphram mounted in avibratory holder and out of contact with the electrodes. The vibratoryholder is activated during the reaction to vibrate or otherwise agitatethe particles and maintain them in a relatively fluidized state. Theelectrodes are generally maintained in close proximity to the particlesbeing treated. Typically the electrodes are at a distance of about 9% to2% cm. from one another depending on the potential applied and theconfiguration of the apparatus used.

In accordance with one embodiment of this invention, a suitable reactionvessel containing particles to be treated is evacuated to a pressure ofthe order of about 0.5 to 3 mm. of mercury. After evacuation, anon-reactive or inert gas such as helium or nitrogen is bled into theapparatus to increase the pressure to about 1 to 5 mm. of mercury. Aircan also be used as the gas. The vibratory holder is activated such thatthe particles are maintained in a thoroughly agitated condition whilethey are being treated. The power source is activated to produce an evenglow between the two substantially parallel plate electrodes. This glowdischarge treatment results in the formation of a substantiallycrosslinked outermost shell of the polymeric binder material of thetoner particles. This crosslinking of the polymer results in asubstantial increase in the minimum caking temperature of the tonerparticles. In general, the increased minimum caking temperature is atleast about 5 to 10 C over that of the untreated toner particles. Theterm minimum caking temperature" has reference to the temperature atwhich the particles become sintered together to such an extent that theycannot be broken apart by gently shaking. Typical materials treated inaccordance with this invention can be stored for periods in excess often hours at temperatures of at least 50 to 55 C with no substantialsintering occurring. Preferred materials can be stored at temperaturesof about 60 to 75 C without substantial caking.

In another embodiment of this invention, a plurality of suitableparticles of resin and colorant are provided in a reaction vessel asdescribed above. Once again, the reaction vessel is evacuated and thistime a gaseous polymerizable material is bled into the apparatus untilthe pressure is of the order of l to 5 mm. of mercury. Then a potentialis applied to the electrode to cause glow discharge. During the glowdischarge treatment, the particles are maintained between the electrodesin an agitated or fluidized state. This glow discharge treatment resultsin the formation of a thin, continuous layer of glow dischargepolymerized material on said particles. This layer changes both thetriboelectric properties of the toner and the minimum caking temperatureof the toner. In general, this layer is extremely thin and difficult tomeasure. The thickness is believed to be less than about 0.2 .1. andpossibly even as thin as about 0.01 2.

Useful gaseous polymerizable materials can be selected from a widevariety of vaporizable monomers or polymer precursors. Suitablematerials would include such monomers as trifluoromonochloroethylene,hexafiuoropropylene, tetrafluoroethylene, octafluorobutene-2, vinylfluoride, vinylidene fluoride, hexafluoroacetone, acrylonitrile,styrene, ethylene, vinyl chloride, methyl methacrylate, divinylbenzene,carbon tetrachloride, hexafluoroethane, vinyl ferrocene, etc, as well asmaterials which are not generally considered as polymer precursors suchas benzene, naphthalene, anthracene, etc. In addition, mixtures of theseor any other vaporizable polymer precursors which undergo polymerizationin the presence of activating radiation can be used. In general, ithasbeen found that when a gaseous polymer precursor as described aboveis polymerized in accordance with the techniques described herein, it ispreferred to keep the particles in motion. Any suitable means formingany such motion can be used. By maintaining the particles in arelatively fluidized condition, a relatively uniform layer of glowdischarge polymerized material is insured. Similarly, when tonermaterials are subjected to glow discharge in the presence of an inertatmosphere or air, it is preferred that the particles be thoroughlyagitated to insure uniform crosslinking of the outermost shell of theindividual particles. However, useful results can be obtained withoutthorough agitation of the particles.

Developer compositions for developing electrostatic charge patterns canbe prepared by admixing the present toner particles with a suitablecarrier material. Typical developer compositions contain from about 1 to10 percent by weight of the present toner with from about 99 to percentby weight of carrier vehicle. The carrier vehicle which can be used withthe present toners to form new developer compositions can be selectedfrom a variety of materials. Suitable carriers useful in this inventioninclude various non-magnetic particles such as glass beads, crystals ofinorganic salts such as sodium or potassium chloride, hard resinparticles, metal particles, etc. In addition, magnetic carrier particlescan be used in connection with this invention. Suitable magneticcarriers are particles of ferromagnetic materials such as iron, cobalt,nickel and alloys thereof. Other magnetic carriers that can be used areresin particles coated with a thin, continuous layer of a ferromagneticmaterial as disclosed in Miller, U. S. application Ser. No. 699,030,filed Jan. 19, 1968, entitled METAL SHELL CAR- RlER PARTlCLES, nowabandoned. The carrier particles used typically have an average particlesize between about 1,200to 30p. depending on the size of the tonerparticles used. Preferred carriers have a particle size of about 600 to4011..

The toner and developer compositions of this invention can be used in avariety of ways to develop electrostatic charge patterns orelectrostatic latent images. Such developable charge patterns can beprepared by a number of means and can be carried on either anelectrophotographic element or on a non-sensitive element such as areceiver sheet. One suitable technique involves cascading the developercomposition across the electrostatic charge pattern; while anothertechnique involves applying toner particles from a magnetic brush. Thislatter technique requires the use of a magnetically attractable carriervehicle in forming the developer composition. After imagewise depositionof the toner particles, the image can be fixed by heating the toner tocause it to fuse to the substrate carrying the toner. If desired, theunfused image can be transferred to another support and then fused toform a permanent image.

The following examples are included for a further understanding of theinvention.

EXAMPLE 1 A toner material is prepared by mixing 62 percent by weight ofPiccolastic D125 (a polystyrene resin, Pennsylvania industrial ChemicalCo.) and 20.6 percent by weight of a rosinmodified maleic resin bymelt-blending. During the meltblending procedure, 9.0 percent by weightof black colorant is incorporated into the mixture. The melt-blendedmixture is allowed to cool to room temperature and is ground such thatit will pass through a 20 mesh U. S. Standard Sieve Series screen. The20 mesh material is then ground in a fluid energy mill to a maximumparticle size of about 20 microns. Next, a developer composition isprepared by mixing 3 grams of this control toner with 97 grams of ironcarrier particles having an average particle size of about 100 to 140microns. An electrophotographic element is provided which comprises aconductive layer having coated thereon a polycarbonate binder containingan organic photoconductor. This element is subjected to a negativepolarity corona discharge while maintained in the dark. The negativelycharged element is then given an imagewise exposure to a photographicpositive which results in the formation of an electrostatic chargepattern. The developer composition prepared as above is placed on asmall magnet to form a magnetic brush. The magnetic brush is lightlyrubbed over the electrostatic charge pattern and toner is deposited onlyin the unexposed areas of the photoconductor. This method of depositionindicates that few, if any, particles have acquired a negative charge.The measurement of the charge on this toner indicates the net charge is+l microcoulombs per gram.

EXAMPLE 2 A sample of the control toner prepared as in Example 1 isplaced on a piece of filter paper contained within a polymeric holdercapable of vibrating the toner material so as to maintain it in afluidized state. This holder is placed between two parallel electrodescomprised of circular stainless steel discs about 2%. cm. in diameterand mounted about 2% cm. apart such that they are above and below thefluidized bed of toner.

This apparatus is contained within an evacuable reaction vessel. Thevessel is evacuated to a pressure of about 0.6 mm. of mercury and thepressure is then increased to 1.5 mm. of mercury by bleeding helium intothe reaction vessel followed by bleeding tetrafluoroethylene into thevessel to increase the pressure to 2.5 mm. of mercury. A 10 kc. a.c.field sufficient to produce a glow at a current of 60 ma. is appliedacross the electrodes for a period of 8 minutes. The electricalequipment used to produce this field is comprised of an audiooscillator, a ZOO-watt audio amplifier and a step-up transformer. A1,000- ohm current limiting resistor is placed in the line to one of theelectrodes and the voltage drop across this resistor is recorded andused to calculate the current. The glow discharge treatment in thehelium-tetrafluoroethylene atmosphere causes the toner particles toattain a net negative charge of 5.4 microcoulombs per gram. This treatedtoner material is then mixed with carrier particles as in Example 1 andused to develop an electrostatic charge pattern prepared by negativelycharging a photoconductive element and imagewise exposing to aphotographic negative. Toner particles are deposited in the exposed(image) areas of the photoconductor indicating that the toner charge ispredominantly negative.

EXAMPLE 3 A toner is prepared using about 30 grams of polystyrenedissolved in about 390 cc. of dichloromethane containing about 2% gramsof Nigrosine Spirit Jet added as a colorant. The resultant combinationis then spray dried through a pneumatic spray nozzle using nitrogen asthe atomizing gas at ambient temperature and at a pressure of about 10psig. to produce uniform particles having a maximum diameter of about 10microns. This control toner is used as in Example 1 to develop anelectrostatic charge pattern formed on a negatively chargedphotoconductive element which has been exposed to a photographicpositive. As in Example 1, no negatively charged particles are observedin that the toner deposits only in the areas of no exposure.

EXAMPLE 4 The toner material prepared as in Example 3 is placed within areaction vessel and treated with a glow discharge in the presence of aheliumtetrafluoroethylene atmosphere in the manner described in Example3 above. This treatment results in the formation of particles which,when mixed with the iron carrier, attain a negative charge with respectto the carrier. This negative charge is evident by the deposition oftoner particles only in the areas of exposure (non-image areas) whenapplied to a negative polarity electrostatic charge pattern as describedin Example 1.

EXAMPLE 5 The control toner of Example 3 is exposed to glow discharge inthe presence of a nitrogen atmosphere at a pressure of about l.5 mm. ofmercury in accordance with the general procedure described in Example 2.When this toner is used to develop a negative electrostatic chargepattern, no difference is seen between this treated toner and thecontrol toner of Example 3 as far as toner charge is concerned. However,the treated toner has a significant increase in resistance to caking onstorage at elevated temperatures. On storage for 15 hours at about 61 Cno caking occurred with this treated toner. The untreated toner ofExample 3 exhibits severe caking when stored under these conditions.

EXAMPLE 6 A toner composition is prepared by melt-blending about 48grams of a polyamide resin binder with about 2.88 grams of carbon blackas a colorant. The mixture is cooled to room temperature and ground to asize such that it will pass through a 20 mesh U. S. Standard SieveSeries screen. The ground material is then further ground in a fluidenergy mill at a 50 psig. air pressure which reduces the particle sizesuch that the maximum diameter is about 20 microns. About 0.5 gram ofthis toner material is then placed in a reaction vessel such asdescribed in Example 1. The toner is placed on a piece of filter papercovering an electrically grounded horizontal square stainless steelelectrode. A high voltage electrode having the same dimensions as thegrounded electrode is positioned about I cm. above the groundedelectrode. The reaction vessel is evacuated to a pressure of about 0.6mm. of mercury and helium is bled into the vessel to a pressure of about2.4 mm. of mercury. Next, a kc. a.c. field sufficient to produce a glowat a current of 60 ma. is applied between the electrodes for 5 minutes.The particles are removed, placed in a container and stored for 18 hoursat about 65 C. A similar amount ofidentical toner which has not beensubjected to glow discharge is also stored in the same condition. Thetreated sample shows some slight clumping after storage; however, theclumps are easily broken by light shaking of the container. Theuntreated control shows considerable caking after storage in theseconditions. Similar treated and untreated materials are stored for l5hours at about 7 l C. The treated sample shows some caking but caneasily be broken up. However, the control shows formation of a hard cakewhich is very difficult to break up.

EXAMPLE 7 A 0.5 gram portion of the toner material of Example 6 isplaced in the glow discharge apparatus and the apparatus is evacuated toa pressure of 0.5 mm. of mercury. The pressure is increased to 1 mm. ofmercury by the addition of helium and then increased further to 2.5 mm.of mercury by introducing tetrafluoroethylene in the reaction vessel. Aglow discharge is produced as in the precedingexample for a period oftwo minutes. The resultant treated toner particles and a similarlyconstituted untreated control are stored for 18 hours at about 66 C. Theuntreated control shows considerable clumping; whereas, the treatedsample shows only slight clumping and is readily broken up by shaking. Asimilar treated toner material and a corresponding control are storedfor l5 hours at about 71 C. Again, the control toner is severely caked;whereas, the treated sample shows only slight caking and can readily bebroken up by gently shaking.

EXAMPLE 8 A sample of the control toner of Example 3 and a sample of thetreated toner of Example 4 are stored for hours at about 60 C. Thetreated sample of Example 4 shows some settling, but no cakingwhatsoever. On the other hand, the control toner of Example 3 showssevere caking and is not readily broken up.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

We claim:

1. A method of treating toner particles for use in the development ofelectrostatic charge patterns comprising the steps of:

a. providing a plurality of particles comprised of a colorant and athermoplastic polymeric binder material,

b. agitating said particles between two substantially parallelelectrodes contained within an evacuated reaction vessel,

c. introducing a gaseous polymerizable material into said vessel and d.establishing a glow discharge between said electrodes while maintainingsaid particles in an agitated state whereby a thin, continuous film ofpolymer is deposited over each particle.

2. A particulate, electroscopic toner composition comprising particlescontaining a colorant and a thermoplastic polymeric binder material,each of said particles having coated thereon a thin, continuous layer ofa glow discharge polymerized material.

. A toner composition as descrtbed in claim 2 wherein said layer ofpolymerized material is formed from a gaseous polymerizable materialselected from the group consisting of trifluoromonochloroethylene,hexafluoropropylene, tetrafluoroethylene, octafluorobutene-Z, vinylfluoride, vinylidene fluoride, hexafluoroacetone, acrylonitrile,styrene, ethylene, vinyl chloride, methyl methacrylate, divinylbenzene,vinyl ferrocene, carbon tetrachloride, hexafluoroethane, benzene,naphthalene, anthracene and mixtures thereof.

4. A toner composition for use in the development of electrostaticcharge patterns comprising particles of a thermoplastic binder havingtherein a colorant, each of said particles having coated thereon a thin,continuous layer of glow discharge polymerized tetrafluoroethylene.

5. A toner composition as described in claim 4 wherein said layer ofglow discharge polymerized tetrafluoroethylene has an average thicknessof less than about 0.2 microns.

6. A developer composition for use in developing electrostatic chargepatterns comprising a mixture of about to 99 percent by weight of aparticulate carrier vehicle and about 10 to 1 percent by weight of atoner material comprised of particles of a thermoplastic polymericmaterial having therein a colorant, each of said particles having coatedthereon a thin, continuous layer of glow discharge polymerized material.

7. A developer composition as described in Claim 6 wherein said tonerhas an average particle size of about /2 to about 25 microns and has aminimum caking temperature in excess of about 55C.

8. A developer composition for use in developing electrostatic chargepatterns comprising a mixture of about 90 to 99 percent by weight of amagnetically responsive particulate carrier vehicle and about 10 to 1percent by weight of a toner material comprised of particles of athermoplastic polymeric material having therein a colorant, each of saidparticles having coated thereon a thin, continuous layer of glowdischarge polymerized material, said layer formed from a gaseouspolymerizable material selected from the group consisting oftrifluoromonochloroethylene, hexafluoropropylene, tetrafluoroethylene,octafluorobutene-2, vinyl fluoride, vinylidene fluoride,hexafluoroacetone, acrylonitrile, styrene, ethylene, vinyl chloride,methyl methacrylate, divinylbenzene, vinyl ferrocene, carbontetrachloride, hexafluoroethane, benzene, naphthalene, anthracene andmixtures thereof.

2. A particulate, electroscopic toner composition comprising particlescontaining a colorant and a thermoplastic polymeric binder material,each of said particles having coated thereon a thin, continuous layer ofa glow discharge polymerized material.
 3. A toner composition asdescribed in claim 2 wherein said layer of polymerized material isformed from a gaseous polymerizable material selected from the groupconsisting of trifluoromonochloroethylene, hexafluoropropylene,tetrafluoroethylene, octafluorobutene-2, vinyl fluoride, vinylidenefluoride, hexafluoroacetone, acrylonitrile, styrene, ethylene, vinylchloride, methyl methacrylate, divinylbenzene, vinyl ferrocene, carbontetrachloride, hexafluoroethane, benzene, naphthalene, anthracene andmixtures thereof.
 4. A toner composition for use in the development ofelectrostatic charge patterns comprising particles of a thermoplasticbinder having therein a colorant, each of said particles having coatedthereon a thin, continuous layer of glow discharge polymerizedtetrafluoroethylene.
 5. A toner composition as described in claim 4wherein said layer of glow discharge polymerized tetrafluoroethylene hasan average thickness of less than about 0.2 microns.
 6. A developercomposition for use in developing electrostatic charge patternscomprising a mixture of about 90 to 99 percent by weight of aparticulate carrier vehicle and about 10 to 1 percent by weight of atoner material comprised of particles of a thermoplastic polymericmaterial having therein a colorant, each of said particles having coatedthereon a thin, continuous layer of glow discharge polymerized material.7. A developer composition as described in claim 6 wherein said tonerhas an average particle size of about 1/2 to about 25 microns and has aminimum caking temperature in excess of about 55*C.
 8. A developercomposition for use in developing electrostatic charge patternscomprising a mixture of about 90 to 99 percent by weight of amagnetically responsive particulate carrier vehicle and about 10 to 1percent by weight of a toner material comprised of particles of athermoplastic polymeric material having therein a colorant, each of saidparticles having coated thereon a thin, continuous layer of glowdischarge polymerized material, said layer formed from a gaseouspolymerizable material selected from the group consisting oftrifluoromonochloroethylene, hexafluoropropylene, tetrafluoroethylene,octafluorobutene-2, vinyl fluoride, vinylidene fluoride,hexafluoroacetone, acrylonitrile, styrene, ethylene, vinyl chloride,methyl methacrylate, divinylbenzene, vinyl ferrocene, carbontetrachloride, hexafluoroethane, benzene, naphthalene, anthracene andmixtures thereof.